U.S. patent application number 17/748855 was filed with the patent office on 2022-09-01 for method, system, and gateway for linking time-sensitive fieldbuses.
This patent application is currently assigned to WAGO Verwaltungsgesellschaft mbH. The applicant listed for this patent is WAGO Verwaltungsgesellschaft mbH. Invention is credited to Fabian SCHWAMBORN.
Application Number | 20220278872 17/748855 |
Document ID | / |
Family ID | 1000006387442 |
Filed Date | 2022-09-01 |
United States Patent
Application |
20220278872 |
Kind Code |
A1 |
SCHWAMBORN; Fabian |
September 1, 2022 |
METHOD, SYSTEM, AND GATEWAY FOR LINKING TIME-SENSITIVE
FIELDBUSES
Abstract
A method and system for networking a first time-sensitive field
bus with a second time-sensitive field bus, the first
time-sensitive field bus comprising a first subscriber device and
having a first dedicated time domain and the second time-sensitive
field bus comprising a second subscriber device and having a second
dedicated time domain, the first and the second field buses being
connected to each other with the aid of a gateway for data
transmission.
Inventors: |
SCHWAMBORN; Fabian; (Loehne,
DE) |
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Applicant: |
Name |
City |
State |
Country |
Type |
WAGO Verwaltungsgesellschaft mbH |
Minden |
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DE |
|
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Assignee: |
WAGO Verwaltungsgesellschaft
mbH
Minden
DE
|
Family ID: |
1000006387442 |
Appl. No.: |
17/748855 |
Filed: |
May 19, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2020/082943 |
Nov 20, 2020 |
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17748855 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 12/4035 20130101;
H04L 7/0008 20130101 |
International
Class: |
H04L 12/403 20060101
H04L012/403; H04L 7/00 20060101 H04L007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 20, 2019 |
DE |
10 2019 217 909.6 |
Claims
1. A method for networking a first time-sensitive field bus with a
second time-sensitive field bus, the first time-sensitive field bus
comprising a first subscriber device and a first dedicated time
domain, and the second time-sensitive field bus comprising a second
subscriber device and a second dedicated time domain, the first and
the second field buses being connected to each other via a gateway
for data transmission, the method comprising: defining the first
time domain in the first field bus via the first subscriber device
of the first field bus; defining the second domain in the second
field bus via the second subscriber device of the second field bus;
transmitting time-sensitive data in defined first time slots within
the first field bus; transmitting time-sensitive data in defined
second time slots within the second field bus; and synchronizing
the gateway as a slave with respect to the first time domain of the
first field bus and additionally with respect to the second time
domain of the second field bus, the gateway supporting at least two
time domains simultaneously.
2. The method according to claim 1, further comprising:
transmitting non-time-sensitive data at a time to the gateway
outside the first time slots of the first field bus; buffering the
non-time-sensitive data in the gateway; and transmitting the
non-time-sensitive data received from the first field bus from the
gateway to the second field bus at a time outside the second time
slots.
3. The method according to claim 1, wherein the following is
provided between the first time domain and the second time domain:
a time offset; different frequencies; different cycle time
durations; different durations of the first and second time slots;
and/or time differences between the first and second time
slots.
4. The method according to claim 1, wherein the gateway comprises a
first timer and a second timer, and wherein the method further
comprises: synchronizing the first timer as a slave with the first
time domain of the first field bus; and synchronizing the second
timer as a slave with the second time domain of the second field
bus.
5. The method according to claim 4, wherein the method further
comprises: initially synchronizing only the frequency of the first
timer of the gateway to the frequency of the second time domain of
the second timer of the gateway; and setting the first timer of the
gateway as the master for the first field bus to set the frequency
of the first field bus to the frequency of the second time
domain.
6. The method according to claim 5, wherein the method further
comprises: determining a cycle time duration of the first time
domain and a cycle time duration of the second time domain via the
gateway at a reference time point; determining a time offset
between the first time domain and the second time domain via the
gateway at a reference time point; communicating the cycle time
duration of the first time domain to the second field bus;
communicating the cycle time duration of the second time domain to
the first field bus; and communicating the time offset to the first
and second field buses with respect to the reference time
point.
7. The method according to claim 6, wherein the method further
comprises: defining the first time slot in the first field bus for
communicating time-critical data via the first subscriber device of
the first field bus; and defining the second time slot in the
second field bus for communicating time-critical data via the
second subscriber device of the second field bus, wherein the
definitions take place such that the time slots of the first field
bus and the second field bus overlap in time.
8. The method according to claim 7, wherein the method further
comprises: transferring time-critical data from the second field
bus to the first field bus or vice versa during the temporally
overlapping time slots.
9. A system for networking at least two time-sensitive field buses,
the system comprising: a first time-sensitive field bus, including
a first subscriber device and a first dedicated time domain, the
first time domain containing first time slots for transmitting
time-sensitive data; a second time-sensitive field bus, including a
second subscriber device and a second dedicated time domain, the
second time domain containing second time slots for transmitting
time-sensitive data; and at least one gateway, which interconnects
the first and second field buses for data transmission, wherein the
gateway comprises a first timer, which is configured to be
synchronized as a slave with respect to the first time domain of
the first field bus, and wherein the gateway includes a second
timer, which is configured to be synchronized as a slave with
respect to the second time domain of the second field bus.
10. The system according to claim 9, wherein the gateway comprises
a buffer for buffering non-time-sensitive data of the first field
bus transmitted from the first field bus at a time outside the
first time slot and received from the gateway and to transmit the
buffered data from the gateway to the second field bus outside the
second time slot.
11. The system according to claim 9, wherein the gateway is
configured to receive information about the first and second time
slots of the first and second field buses and to take this
information into account during the transmission of the
non-time-critical data.
12. The system according to claim 9, wherein the subscriber device
of the first field bus is configured to define the first time slot,
wherein the subscriber device of the second field bus is configured
to define the second time slot such that the first and second time
slots overlap in time, and wherein the gateway is configured to
conduct time-critical data from the second field bus to the first
field bus or vice versa during the overlapping first and second
time slots of the first and second field buses.
13. A gateway for networking at least two time-sensitive field
buses having different time domains, the gateway comprising: a
first timer configured to be synchronized as a slave with respect
to the first time domain of the first field bus; and a second timer
configured to be synchronized as a slave with respect to the second
time domain of the second field bus.
14. The gateway according to claim 13, wherein the gateway is
configured for the data transmission of non-time-critical data
between the first field bus and the second field bus at times
outside time slots for time-critical data of the first field bus or
the second field bus, the gateway having a buffer for buffering
received non-time-critical data of a field bus prior to being sent
to the other field bus.
15. The gateway according to claim 13, wherein the gateway is
configured to receive information about time slots of the first
field bus and information about time slots of the second field bus
and to take this information into account while sending data.
16. The gateway according to claim 13, wherein the gateway is
further configured to transfer time-critical data from the second
field bus to the first field bus or vice versa during the
temporally overlapping time slots.
17. The gateway according to claim 16, wherein, during the transfer
of time-critical data, the gateway is configured to take into
account the information about the time slot of the first field bus
and the information about the time slot of the second field bus.
Description
[0001] This nonprovisional application is a continuation of
International Application No. PCT/EP2020/082943, which was filed on
Nov. 20, 2020, and which claims priority to German Patent
Application No. 10 2019 217 909.6, which was filed in Germany on
Nov. 20, 2019, and which are both herein incorporated by
reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to time-sensitive field bus
systems, in particular industrial field bus systems for controlling
industrial systems. In particular, the invention relates to a
method, a system and a gateway for networking at least two
time-sensitive field buses.
Description of the Background Art
[0003] Field buses are used to interconnect different subscriber
devices (e.g., field devices such as sensors, actuators, detectors,
control elements, etc., as well as controllers, such as control or
automation devices, programmable logic controllers (PLCs), etc.) in
a plant (e.g., an industrial manufacturing facility, vehicle,
building, etc.) for the purpose of communication. However, the
communication does not take place, in particular, exclusively
between different field devices and a field bus controller, which
controls and monitors the processes running in the plant. A
subscriber device may be a field device or a controller and has, in
particular, an interface to the field bus.
[0004] The messages to be transmitted via a field bus (e.g., data
blocks, data streams) are at least partially time-sensitive, i.e.,
they have real-time requirements with regard to the transmission
latency. For example, it is necessary for time-sensitive data of
this type that a message sent by a subscriber device is reliably
received by the field bus controller or another field device
connected to the field bus within a predictable period of time.
[0005] The data to be transmitted between subscriber devices of the
field bus comprise not only value communication, such as measured
values, manipulated variables or instructions, but also event
communication for the temporal coordination of machines and plant
parts. For example, the coordination and synchronization of
movements of machine parts increasingly no longer take place via
mechanical apparatuses (e.g., metal presses having mechanically
rigid, coupled feeding and ejecting apparatuses in the machine
cycle, camshafts, gears, etc.), but rather via digital messages,
which are transmitted with real-time requirements via field
buses.
[0006] A field bus is assigned to a time domain, in which all
subscriber devices each have a timer (e.g., a clock). The timers of
the subscriber devices are synchronized with each other within the
time domain and thus have a common understanding of time. All
subscriber devices of a field bus may thus follow a defined field
bus communication cycle and are coordinated with each other to
carry out the corresponding actions at the right point in time. One
subscriber device of the field bus acts as a master for the time
domain, the timer of the master supplying the time reference for
the other subscriber devices of the time domain. The latter
subscriber devices, which derive their time from the master within
the time domain, are also referred to as slaves. The role of the
time master in the field bus may be taken on by a field bus
controller, however also by another subscriber device connected to
the field bus. The time master of the field bus may synchronize its
time base with another time base, for example with the time master
of another field bus or with a hierarchically superordinate time
base. In that the masters of multiple field buses synchronize their
particular field bus time with each other, a time domain may also
comprise multiple field buses. The "clocks" are adjusted by the
synchronization of the time base. However, this does not
necessarily mean that two field buses within one time domain have
the same communication cycles.
[0007] A first generation of field buses was developed to replace
the cabling complexity due to the parallel wiring of machine parts,
which used to be common practice, by means of cable assemblies,
with digital transmission technology. Multiple, in part
proprietary, field bus protocols were developed for this purpose.
Later generations of field buses are based primarily on the
Ethernet standard IEEE 802.3, the Ethernet protocols having been
modified or expanded to implement time-sensitive networks
(TSNs).
[0008] Standards for real-time Ethernet protocols are developed,
for example, by the IEEE 802.1Q task group, for TSN networks. A
time-aware scheduler is defined, for example, by the IEEE802.1QBV
standard. The scheduler makes it possible to divide the
communication in a network into fixed, periodically repeating
communication cycles and to define, reserve or negotiate fixed time
slots for transmitting time-critical data within the cycles. A
clocked end-to-end transmission between two subscriber devices may
be implemented hereby.
[0009] Non-time-sensitive data (best effort data) may be
transmitted outside the time slots provided for real-time
transmission, the known protocols for a packet-switched
transmission (e.g., Ethernet protocol) being used for this purpose.
Guard bands may be configured by the time-aware scheduler to
prevent an overlapping of transmissions of non-time-sensitive data
packets with the time slots reserved for real-time
transmissions.
[0010] In TSN networks, it is furthermore possible to interrupt and
subsequently resume the transmission of non-time-sensitive data
packets during the real-time intervals. The coexistence of
time-sensitive and non-time-sensitive communication is made
possible in this way in a TSN-capable network.
[0011] During the course of the increasing digital transformation
and networking of plants (e.g., of an entire production facility),
it is necessary to facilitate the communication between field buses
as well as the communication between a field bus and equipment of a
higher control level, process control level and/or operating
control level and/or company level. The networking relates to both
non-time-sensitive data and time-sensitive data.
[0012] Although most field buses in use today base real-time
protocols on Ethernet, technical differences do exist despite this
commonality, so that different field bus types are incompatible or
not completely compatible with each other. In addition, different
generations of field buses may be used, for example when parts of a
plant are added, replaced or modernized, field buses of different
generations not necessarily being fully compatible. At present,
efforts are being made to specify universally usable real-time
protocols, which are expected to replace the many proprietary and
incompatible protocols for time-sensitive field buses. However,
their use requires existing field bus system to be replaced or
retrofitted, which is often not economically justifiable.
[0013] Existing approaches for time-sensitive communication between
two or multiple field buses assume that all field buses to be
coupled have a uniform understanding of time, all time offsets as
well as time durations and/or start times of the field bus
communication cycles, however, being synchronized. However, field
buses are often configured in complex ways at the start of
manufacturing, so that the machines controlled by the field bus
and/or plant parts are optimally coordinated with each other. An
adjustment of the cycle times of an existing field bus to newly
added plant parts having further field buses would, however, make
it necessary to reconfigure the existing processes controlled by
the field bus.
[0014] A need therefore exists to interconnect time-sensitive field
buses, which are not completely compatible with each other.
SUMMARY OF THE INVENTION
[0015] It is therefore an object of the present invention to
provide a method for networking a first time-sensitive field bus
with a second time-sensitive field bus, a system for networking at
least two time-sensitive field buses, as well as a gateway for the
purpose of time synchronization and for networking at least two
time-sensitive field buses.
[0016] To achieve the object, in particular, a gateway is used,
which mediates the communication between time-sensitive field
buses. Since the gateway supports the particular time domain of all
field buses connected thereto, the field buses may communicate with
each other largely without adjusting the time and, in particular,
the times of the communication cycles. This applies to
time-sensitive data as well as to non-time-sensitive data.
[0017] An aspect of the present invention relates to a method for
networking a first time-sensitive field bus with a second
time-sensitive field bus. The first time-sensitive field bus
comprises a first subscriber device and has first dedicated time
domain. The second time-sensitive field bus comprises a second
subscriber device and has a second dedicated time domain. The first
and second field buses are connected to each other with the aid of
a gateway for the purpose of data transmission. The method
comprises the definition of the first time domain in the first
field bus by the first subscriber device of the first field bus as
well as the definition of the second time domain in the second
field bus by the second subscriber device of the second field bus,
the transmission of time-sensitive data in defined first time slots
within the first field bus, and the transmission of time-sensitive
data in defined second time slots within the second field bus. The
method furthermore comprises the synchronization of the gateway as
a slave with respect to the first time domain of the first field
bus and additionally with respect to the second time domain of the
second field bus, the gateway supporting at least two time domains
simultaneously. Due to the support for the two time domains, the
gateway is configured to transmit messages or data, such as data
packets, between the field buses in keeping with the communication
cycles defined on the field buses and time slots for sensitive data
without the particular time domains of the field buses having to be
synchronized with respect to the absolute time and the cycle times
of the communication cycles having to be adjusted.
[0018] The method furthermore comprises the steps of transmitting
non-time-sensitive data at a time outside the first time slot from
the first field bus to the gateway, the temporary storage of the
non-time-sensitive data in the gateway as well as the transmission
of the non-time-sensitive data received from the first field bus
from the gateway to the second field bus at a time outside the
second time slot. In this way, non-time-sensitive data may be
transmitted, taking into account the first time slots of the first
field bus and the second time slots of the second field bus defined
on the particular field buses.
[0019] It is possible in practice for there to be a time offset
between the first and second time domains. This time offset results
due to the different definitions of the time of the first and
second time domains as well as from the difference between the
starting times of the communication cycles of the first and second
field buses. The time domains of the field buses may furthermore
have different frequencies. In particular, the clocks of the
subscriber devices have specific clock frequencies, which may be
frequency-synchronized accordingly within a time domain, although
this does not apply between the time domains. Even if the clock
frequencies in the time domains of the first and second field buses
are nominally the same, the local oscillators for the timers may
have slight differences, which result in frequency differences of
the timers. In addition, different time durations for the
communication cycles may be defined in the first and second time
domains, within which the first and second time slots in each case
are periodically repeated for transmitting the time-sensitive data.
Moreover, time differences may exist between the first and second
field buses, e.g., in relation to the first and second time slots
for transmitting time-sensitive data.
[0020] The gateway includes a first and a second timer, and the
method further includes the steps of synchronizing the first timer
as a slave with the first time domain of the first field bus and
synchronizing the second timer as a slave with the second time
domain of the second field bus. As a result, the gateway "knows"
the time defined in the first and second time domains in each case
and may coordinate, for example, the transmission of
non-time-sensitive data in such a way that the time slots for
transmitting time-sensitive data are not affected.
[0021] The frequency of the first timer of the gateway can be first
set exclusively to the frequency of the second time domain of the
second timer of the gateway, and the first timer of the gateway is
set as the master for the first field bus for the purpose of
setting the frequency of the first field bus to the frequency of
the second time domain. In this way, a synchronization of the clock
frequencies may take place in the time domains of the first and
second field buses. Based on a minimal synchronization of this
type, the first and second field buses or the first and second time
domains may have differently defined times, however the time offset
is time-invariant, i.e., constant over time. In particular, due to
only one synchronization of the clock frequency of the timers in
the first and second field buses, a hard abrupt change in time in
the first field bus is avoided, which could occur during the
adjustment of the first and second field bus times. The adjustment
of the frequencies may take place over the time period which does
not impair the operation of the processes controlled in the first
field bus.
[0022] The gateway can determine the cycle time period of the first
time domain and the cycle time period of the second time domain at
a particular reference time following the frequency
synchronization. The latter reference time point may be determined
in relation to the time valid in the first and/or second time
domain(s).
[0023] The gateway may furthermore determine a time offset between
the first time domain and the second time domain at the reference
time point. The time offset includes the differences in the
definition of the time of the first and second time domains as well
the difference between the starting time points of the
communication cycles of the first and second field buses. The
gateway may additionally communicate the cycle time duration of the
first time domain to the second field bus and communicate the cycle
time duration of the second time domain to the first field bus. In
this way, for example, the first subscriber device in the first
time domain or the second subscriber device in the second time
domain is able to determine and continue the cycle time duration
and the time offset in the particular other field bus in relation
to the reference time point.
[0024] The first subscriber device can define a first time slot in
the first field bus for communicating time-critical data, and the
second subscriber device defines a second time slot in the second
field bus for communicating time-critical data, the definition
taking place in such a way that the time slots of the first field
bus and the second field bus overlap in time. The first and second
time slots may be identical (i.e., completely overlap), or they
have at least one temporal intersection to be able to set up a
time-critical communication between the first field bus and the
second field bus.
[0025] Time-critical data passes through the gateway from the
second field bus to the first field bus and/or vie versa during the
temporally overlapping first and second time slots. A clocked
end-to-end transmission between two subscriber devices and is
implemented thereby beyond field bus boundaries.
[0026] A further aspect of the invention relates to a system for
networking at least two time-sensitive field buses, including a
first time-sensitive field bus, which has a first subscriber device
and a first dedicated time domain, the first time domain containing
first time slots for transmitting time-sensitive data. The system
further comprises a second time-sensitive field bus, which has a
second subscriber device and a second dedicated time domain, the
second time domain containing second time slots for transmitting
time-sensitive data. The system furthermore includes at least one
gateway, which connects the first and second field buses to each
other for the purpose of data transmission, the gateway including a
first timer, which is configured to be synchronized as a slave with
respect to the first time domain of the first field bus, and the
gateway including a second timer, which is configured to be
synchronized as a slave with respect to the second time domain of
the second field bus. Due to the support for the two time domains,
the gateway is configured to transmit messages or data, such as
data packets, between the field buses in keeping with the
communication cycles defined on the field buses and time slots for
sensitive data without the particular time domains of the field
buses having to be synchronized with respect to the absolute time
and the cycle times of the communication cycles having to be
adjusted.
[0027] The gateway may include a buffer for buffering
non-time-sensitive data of the first field bus transmitted from the
field bus at a time outside the first time slots and received by
the gateway, and to transmit the buffered data from the gateway to
the second field bus outside the second time slots. This makes it
possible to transmit non-time-sensitive data at times at which the
two field buses are not transmitting time-sensitive data.
[0028] The gateway may also be configured to receive information
via the first and second time slots of the first and second field
buses and to take into account the non-time-critical data during
transmission. This prevents the non-time-critical data from being
sent during a time slot of the second field bus reserved for
time-critical transmission.
[0029] The subscriber device of the first field bus may be
configured to define the first time slots in such a way, and the
subscriber device of the second time slots may be configured to
define the second time slots in such a way that the first and
second times slots overlap in time. The gateway may furthermore be
configured to transfer time-critical data from the second field bus
to the first field bus or vice versa during the overlapping first
and second time slots of the first and second field buses.
[0030] A further aspect relates to a gateway for networking at
least two time-sensitive field buses having different time domains.
The gateway includes a first timer, which is configured to be
synchronized as a slave with respect to the first time domain of
the first field bus, and includes a second timer, which is
configured to be synchronized as a slave with respect to the second
time domain of the second field bus. Due to the support for the two
time domains, the gateway is configured to transmit messages or
data, such as data packets, between the field buses in keeping with
the communication cycles defined on the field buses and time slots
for sensitive data without the particular time domains of the field
buses having to be synchronized with respect to the absolute time
and the cycle times of the communication cycles having to be
adjusted.
[0031] The gateway can be configured for the data transmission of
non-time-critical data between the first field bus and the second
field bus at points in time or during time periods outside time
slots for time-critical data of the first field bus or the second
field bus, the gateway having a buffer for buffering received
non-time-critical data of a field bus prior to being sent to the
other field bus.
[0032] The gateway may also be configured to receive information
about time slots of the first field bus and information about time
slots of the second field bus and to take this information into
account while sending data.
[0033] The gateway may moreover be configured to transfer
time-critical data from the first field bus to the second field bus
or vice versa during overlapping time slots.
[0034] The gateway can be configured to take into account the
information about the time slot of the field bus and the
information about the time slot of the second field bus when
transferring time-critical data.
[0035] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes, combinations and modifications within the spirit and scope
of the invention will become apparent to those skilled in the art
from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus, are
not limitive of the present invention, and wherein:
[0037] FIG. 1 shows a block diagram of a system including a first
time-sensitive field bus and a second time-sensitive field bus;
[0038] FIG. 2 schematically shows a timing diagram of a first and
second field bus as well as the transmission of non-time-sensitive
data through the gateway;
[0039] FIG. 3 schematically shows a detailed timing diagram of the
cycle times defined for the first and second field buses; and
[0040] FIG. 4 schematically shows a timing diagram of a first and
second field bus as well as the transmission of time-sensitive data
through the gateway.
DETAILED DESCRIPTION
[0041] FIG. 1 shows a block diagram of an exemplary system 1
including a first time-sensitive field bus 10 and a second
time-sensitive field bus 20. First field bus 10 and second field
bus 20 comprise, for example, subscriber devices 12, 14a-c or 22,
24a-c, subscriber devices 12, 22 each being controllers of the
field bus, for example an automation device, a programmable logic
controller, PLC, a node or another industrial controller, and
subscriber devices 14a-c or 24a-c being field devices, for example
I/O modules for sensors and/or actuators, which may measure or
influence variables of a process automated by the field bus.
Subscriber devices 12, 14a-c or 22, 24a-c are communicatively
connected to each other in particular field bus 10, 20 via an
interface, the definition of the interface comprising an interface
protocol.
[0042] Subscriber devices 12, 14a-c of first field bus 10 belong to
a first time domain 16, all subscriber devices 12, 14a-c having the
same understanding of an absolute time. For this purpose, each
subscriber device 12, 14a-c has a timer, which is schematically
symbolized in FIG. 1 by the face of a clock. Subscriber devices 22,
24a-c of second field bus 20 correspondingly belong to a second
time domain 26. In field buses 10 and 20, the field bus lines
emerging from controller 12, 22 are connected to the field buses in
a star shape. Field buses may also generally be formed by other
topologies, such as a tree topology, bus topology, ring topology.
It is also possible that subscriber devices 12, 24a-c or 22, 24a-c
of a field bus 10, 20 are at least partially connected to each
other by a wireless network.
[0043] One subscriber device 12, 24a-c or 22, 24a-c in each case
predefines the time for particular field bus 10 or 20 and is
therefore referred to as the master. In first field bus 10,
controller 12, for example, is the master, which is represented by
solid lines in FIG. 1 as a clock face. In second field bus 20,
subscriber device 24a, for example, is the field bus master. The
clock of a master 12 or 24a predefines the time in the field bus in
each case, the remaining subscriber devices of a field bus, i.e.,
subscriber devices 14a-c in the first field bus or subscriber
devices 22, 24b-c, each derive their time from the master. This is
done, for example, in that the subscribers within a field bus
exchange messages at regular or irregular intervals according to
the Precision Time Protocol according to the IEEE 1588 standard and
thus obtain and maintain a common understanding of the time in this
way.
[0044] Within first field bus 10 and second field bus 20,
non-time-sensitive as well as time-sensitive data may be
transmitted in each case, as is described in greater detail below.
For example, the data transmission in both field buses may be
divided into transmission cycles according to the IEEE 802.1Q
standard, first time slots in first field bus 10 and second time
slots in second field bus 20 being defined, in which a clocked
end-to-end transmission is possible between two subscriber devices
of the same field bus in each case.
[0045] System 1 further comprises a gateway 30, via which both
field buses 10, 20 are communicatively connected to each other.
Although FIG. 1 shows that field buses 10, 20 are connected to each
other via their controllers 12 and 22, this is not mandatory.
Instead, gateway 30 has an interface to each of field buses 10 and
20, so that it represents a subscriber device with respect to
particular field bus 10, 20. Gateway 30 supports at least two time
domains 32 and 34. Further time domains may be supported according
to the number of field buses to be coupled. In particular, the
gateway comprises timers 36 and 38, which may be configured for
first time domain 16 or for second time domain 26.
[0046] Gateway 30 may interconnect first field bus 10 and second
field bus 20 for the purpose of data transmission. For this
purpose, gateway 30 maintains a memory 35 for buffering or
temporarily storing data. For example, non-time-sensitive data may
be stored in memory 35. However, gateway 30 may also transfer a
clocked end-to-end transmission between first and second field
buses 10, 20 during defined time slots without a delay.
[0047] FIG. 2 shows an example of a timing diagram of first field
bus 10 and second field bus 20. First field bus 10 has
communication or transmission cycles with periodically recurring
cycle intervals TC1, which are defined by location and duration
according to the upper timeline in FIG. 2. Second field bus 20
correspondingly has communication cycles with periodically
recurring cycle intervals TC2, which are defined by location and
duration according to the lower timeline in FIG. 2.
[0048] In field buses 10, 20, first time slots 50 or second time
slots 52 may be defined, negotiated or ascertained for transmitting
time-sensitive data within particular field bus 10, 20. For
example, the time-aware scheduler defined in the IEEE 802.1QBv
standard may be used for this purpose. First time slots 50 and
second time slots 52 coincide with the start of corresponding
communication cycles only by way of example. Time slots 50, 52 may
generally be situated at any position within a transmission cycle
for time-sensitive transmission. It is also possible to define
multiple separate time slots 50, 52 per transmission cycle for a
time-sensitive communication.
[0049] FIG. 2 also shows time periods 54 and 56, which belong to
the particular transmission cycles, which are situated outside time
slots 50 or 52 reserved for transmitting time-sensitive data. At
these intervals 54, 56, non-time-sensitive data may be transmitted
between field buses 10, 20, for example according to the Ethernet
protocol, to which the CSMA/CD (carrier-sense multiple access with
collision detection) access method applies.
[0050] In an example, timers 36 and 38 of gateway 30 are first
synchronized as slaves with respect to time domains 16, 26 of field
buses 10 and 20. Since gateway 30 has an interface as a subscriber
device to first field bus 10 as well as second field bus 20,
corresponding cycle time durations TC1 and TC2, the temporal
location of the communication cycles as well as time slots 50 and
52, in which time-sensitive communication is handled in particular
field buses 10, 20, are known on the part of gateway 30.
[0051] Correspondingly, intervals 54 and 56 which transmit
non-time-sensitive data are also known.
[0052] A transmission of non-time-sensitive data between first
field bus 10 and second field bus 20 may take place in that
non-time-sensitive data 60 are transmitted from first field bus 10
to gateway 30 during a first non-time-sensitive interval 54, as
symbolized by arrow 60. These data 60 may be buffered in buffer 35
of gateway 30, as symbolized by step 62. Finally, the buffered data
may be transmitted from gateway 30 to second field bus 20 during
intervals 56 outside second time slots 52, as symbolized by arrow
64. For example, to send data 64 to the second field bus with the
aid of the CSMA/CD method or another contention method, gateway 30
must ensure that second field bus 20 is free for transmission
during time slots 56.
[0053] FIG. 3 schematically shows a detailed timing diagram of the
cycle times defined for first and second field buses 10, 20
according to some aspects of the invention. In one example, the
timers in the subscriber devices of field buses 10 and 20 may have
different clock frequencies f1 or f2. In FIG. 3, the reciprocal
value of clock frequencies 1/f1 or 1/f2, namely the clock cycle
duration, is illustrated in each case by a black bar. Even if both
clock frequencies f1 and f2 nominally have the same frequencies
(i.e., according to a specification), the clocks of time domains 16
and 26 of the two field buses run at different speeds, if the
actual values of clock frequencies f1 and f2 differ slightly from
each other.
[0054] Moreover, a time offset 58 may occur between the starting
time points of the communication cycles. A time offset 58 of this
type results, on the one hand, due to the different definitions of
the time in the two field buses 10, 20, and, on the other hand,
from the difference between the starting time points of the
communication cycles of first field bus 10 and second field bus 20,
even if both field buses were to have the same understanding of
time. The communication cycles may also have different durations
TC1 and TC2. Time offset 58 may therefore generally be defined only
with respect to an (absolute) reference time point TRef. Absolute
reference time point TRef may be expressed accordingly in the time
of first field bus 10 as well as in the time of second field bus
20. If time durations TC1 and TC2 are in a rational relationship to
each other, a particular time offset 58 recurs after a predictable
number of cycles of the first or second field bus. For example, if
cycle time duration TC1 in the first field bus is 50 ms, and cycle
time duration TC2 in the second field bus is 25 ms, for example,
time offset 58 may be zero in the second field bus after a first
cycle, 25 ms with respect to the first field bus in the second
field bus, and then zero again, etc. However, if time offset 58 is
known at a point in time TRef, it is possible to determine time
offset 58 in advance for all communication cycles of the first and
second field buses, even if cycle time durations TC1 and TC2 are
not in a rational relationship to each other.
[0055] Moreover, different durations TS1 and TS2 of first and
second time slots 50 and 52 may occur on field buses 10 and 20 for
the time-sensitive communication, since they may be specified
independently of each other for both field buses 10 and 20. In
addition, first and second time slots 50 and 52 may have time
differences TD in terms of their start times. These, in turn, may
generally be predictably determined only with respect to an
absolute reference time point TRef, since start times of time slots
50 and 52 may vary for the time-sensitive communication with the
cycle times in the individual field buses.
[0056] According to an example, as described above, first timer 36
of gateway 30 is configured as a slave of first field bus 10, and
second timer 38 of gateway 30 is configured as a slave of second
field bus 20. To simplify the communication between first and
second field buses 10, 20, it may now be useful to synchronize only
frequencies f1 and e2 of first time domain 16 and second time
domain 26. Due to such a synchronization of the timer clock
frequencies, the time offset between the time of the two time
domains 16 and 26 remains stable, whereby the determination of
points in time in gateway 30 or in subscriber devices 12, 14a-c or
22, 24a-c of the first and second field buses is simplified with
respect to the other time domain 16, 26 in each case. The timers of
both time domains 16, 26 have the same nominal frequency. A
frequency synchronization may take place only in that first timer
36 of gateway 30 is determined as the master for first field bus
10, so that gateway 30 is able to make a determination by setting
the time in the first field bus. Furthermore, a synchronization of
frequency f1 of first timer 36 of gateway 30 may be made to
frequency f2 of second time domain 26. A synchronization
exclusively of frequencies f1 and f2 in time domains 16, 26, it may
be sensible to avoid abrupt changes in time of the subscriber
devices in first field bus 10. The frequency may be synchronized
during the operation of first field bus 10 via an adjustment time
duration, which is selected to be long enough for the processes of
first field bus 10 to run without disturbances.
[0057] After the frequencies have been synchronized, gateway 30 may
determine cycle time durations TC1 and TC2 of first and second time
domains 16, 26 at a reference time point TRef. Gateway 30 may
furthermore determine time offset 58 between first and second time
domains 16, 26 at a reference time point TRef. Gateway 30 may
additionally communicate cycle time period TC1 of first time domain
16 to second field bus 20 and communicate cycle time period TC2 of
second time domain 26 to first field bus 10. This may take place
with respect to reference time point TRef. In this way, certain
subscriber devices of first or second field bus 10, 20 may
predictably determine the communication cycles of the other field
bus 20, 10 in each case.
[0058] FIG. 4 schematically shows a timing diagram of a first field
bus 10 and a second field bus 20 during a transmission of
time-sensitive data. Since cycle time durations TC1 and TC2 of
first and second time domains 16, 26 are known in both field buses
at a reference time point TRef, subscriber device 14c of first
field bus 10, for example, may transmit time-sensitive data to
subscriber device 24b of second field bus 20. This may take place
in that subscriber devices 14c and 24b define time slot 50, 52 in
particular field bus 10, 20 for the communication of time-critical
data, which at least partially overlap. For example, subscriber
devices 14c and 24b may exchange possible time intervals for a
time-sensitive communication within the scope of negotiations if
they are configured to do so (e.g., as schedulers according to the
IEEE802.1QBv standard). For example, subscriber device 14c may send
a request to subscriber device 24b to query possible time intervals
and then determine a common time interval. It is also possible that
subscriber device 14c and/or subscriber device 24b has/have the
determination of first or second time slot 50, 52 for the
communication of time-critical data representatively carried out by
another subscriber device of first or second field bus 10, 20
configured for this purpose.
[0059] In the present example according to FIG. 4, corresponding
subscriber devices of the first and second field buses have
specified common overlapping areas OL1 and OL2 in time slots 50 and
52 and have exchanged this information via gateway 30, so that it
is also known to gateway 30. It is also possible that corresponding
time slots 50 and 52 are shifted relative to the cycle interval of
the particular first or second field bus in the particular cycles
for the time-sensitive communication, so that an overlapping area
OL1 or OL2 may be generated in each cycle.
[0060] It is not necessary to generate an overlapping area OL1, OL2
for the time-sensitive communication in each cycle TC1 or TC2 of
first or second field bus 10, 20. For example, it may be sufficient
to define an overlapping area during each second, third, etc. cycle
of first or second field bus 10, 20.
[0061] If first and second time slots 50 and 52 are known during
the communication cycles of first and second field buses 10, 20,
which are reserved for a time-sensitive communication within the
field buses, overlapping areas OL1 and OL2 may be determined or
calculated in a rule-based manner for a time-sensitive
communication between the field buses. It is then sufficient to
determine a single pair of overlapping time slots 50 and 52 at a
reference time point TRef.
[0062] If cycle time durations TC1 and TC2 have a rational
relationship to each other, recurring overlapping areas OL1 and OL2
result on a regular basis. In this case, the negotiation and/or
determination of time slots 50 and 52 is/are made easier, so that
in these cases an overlapping area OL1, OL2 recurs regularly and
therefore does not have to be negotiated or determined
individually. The gateway 30 is further configured to transmit
time-critical data 70, 72 during the temporally overlapping time
slots, e.g., OL1 and OL2. In an example, this takes place in that
gateway 30 ascertains the time slots for time-sensitive
transmission 50 and 52 ascertained between first and second field
buses 10, 20 and, in particular, particular overlapping areas OL1,
OL2 and conducts the signals between the first and second field
buses during these intervals.
[0063] Due to the described method, system 1 and gateway 30, it is
possible to network time-sensitive field buses 10, 20 without
having to carry out an adjustment of the field bus times as well as
the communication cycles of the field buses. In particular,
existing and, in part incompatible, field buses may be configured
thereby to exchange non-time-sensitive data s well as to exchange
time-sensitive data.
[0064] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are to be included within the scope of the following
claims.
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